1. Field of the Invention
The present invention relates to high frequency antennas, and more particularly to an EHF antenna having a shaped lens that produces a nearly uniform transmission signal coverage over a hemispherical coverage area.
2. Brief Description of the Prior Art
In space vehicle communications, the telemetry, tracking, and command (TT&C) antenna provides ranging, telemetry, and command operation throughout all mission phases after launch vehicle separation. An ideal requirement for a TT&C antenna is that it be omnidirectional. Although a number of antennas have been designed to generate a nearly omnidirectional beam, there are no such antenna designs suitable for the high frequency EHF band of 40-100 GHz. In practice, an omnidirectional beam is represented by a cardioid pattern. Such a cardioid beam has been generated in lower frequency (four and six GHz) ranges by a slotted-ring antenna, wherein pattern shaping is achieved by using a multi-ring on a cylinder waveguide or by attaching a conical reflector to the waveguide structure. A single conical spiral antenna is another prior art device. However, these types of antennas are too small to successfully fabricate them in the EHF band.
The utilization of a lens to shape the transmission beam pattern of high frequency band signals is well known. U.S. Pat. No. 2,669,657, issued Feb. 16, 1954 to C. C. Cutter; U.S. Pat. No. 3,787,872, issued Jan. 22, 1974 to James F. Kauffman; and U.S. Pat. No. 4,321,604, issued Mar. 23, 1982 to James F. Ajioka; each teach devices that utilize a lens composed of a dielectric material to shape an input beam from a horn antenna. However, the teachings of each of these patents is directed to a lens that focuses a diverging beam from a horn into a parallel beam. As is described in detail hereinbelow, the present invention disburses the diverging beam from a horn antenna into a uniformly disbursed transmission signal covering a hemispherical area.
U.S. Pat. No. 3,434,146, issued Mar. 18, 1969 to L. G. Petrich teaches a dielectric disc lens that is placed in the mouth of a horn to produce a hemispherical transmission pattern. To the inventor's knowledge, it has not been possible to produce such a disc lens that is placed in the far-field of the horn for the EHF frequencies to which the present invention is adapted. Other U.S. Patents such as U.S. Pat. Nos. 2,719,230; 2,761,138; 2,795,783; 3,366,965; 3,550,147; 3,763,493; 3,848,255; 4,636,798; and 4,682,179 all teach electromagnetic lenses of various types. However, the teachings of these patents seem less material to the disclosure of the present invention than those discussed hereinabove.